The Top 10 Nuclear Energy Countries in the World based on capacity in 2015 are shown below:
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Source: GCC–East Asia Relations in the Fields of Nuclear and Renewable Energy: Opportunities and Barriers, Oxford Institute for Energy Studies
The US is the number one country in terms of nuclear energy capacity. However nuclear energy accounts for only 8% of energy consumption in the US as the following chart shows:
France generates most the electricity from nuclear power. The only developing country in the above list is China. It is surprising that China has the same amount of nuclear energy capacity as Russia which is traditionally a super power in nuclear energy and advanced sciences.